Transcription of genes encoding DNA replication proteins is coincident with cell cycle control of DNA replication in Caulobacter crescentus

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Abstract
DNA replication in the dimorphic bacterium Caulobacter crescentus is tightly linked to its developmental cell cycle. The initiation of chromosomal replication occurs concomitantly with the transition of the motile swarmer cell to the sessile stalked cell. To identify the signals responsible for the cell cycle control of DNA replication initiation, we have characterized a region of the C. crescentus chromosome containing genes that are all involved in DNA replication or recombination, including dnaN, recF, and gyrB. The essential dnaN gene encodes a homolog of the Escherichia coli beta subunit of DNA polymerase III. It is transcribed from three promoters; one is heat inducible, and the other two are induced at the transition from swarmer to stalked cell, coincident with the initiation of DNA replication. The single gyrB promoter is induced at the same time point in the cell cycle. These promoters, as well as those for several other genes encoding DNA replication proteins that are induced at the same time in the cell cycle, share two sequence motifs, suggesting that they represent a family whose transcription is coordinately regulated.